In known apparatuses of this kind, a first fluid flows through the main heat exchanger, while a second fluid, which is cooled by the first fluid, flows through the secondary heat exchanger. In the application of such an apparatus to motor vehicles, the first fluid is the cooling liquid for the engine of the vehicle, while the second fluid may for example be lubricating oil for the engine, or gearbox oil, or oil for a torque converter. Thus the engine coolant liquid not only fulfils its usual function of cooling the engine, but also an additional function whereby it cools a further fluid related to the operation of the vehicle.
In known arrangements of this kind, the secondary heat exchanger is introduced through an open side of the water box, and the latter is then secured to the body or the tube bundle of the main heat exchanger. The secondary heat exchanger has two coupling tubes, which serve respectively as input and output tubes for the second fluid, and which extend sealingly through two orifices formed in a wall of the water box. This arrangement also secures and retains the secondary heat exchanger within the water box.
In the specification of French patent application No. 83 12200, published under the number FR-2 549 593-A, there is disclosed an apparatus of the kind described above, in which the two coupling tubes are fitted on to the secondary heat exchanger after the latter has been itself fitted within the water box of the main heat exchanger. Each of the two coupling tubes is then introduced from outside the water box, first through a respective one of the orifices mentioned above and formed in the wall of the water box, and then into an appropriate seating which is part of the second heat exchanger. An advantage of that arrangement is that it enables the external dimensions of the secondary heat exchanger to be made substantially the same as the internal dimensions of the water box; and this in turn enables the efficiency of the secondary heat exchanger to be improved while still using a water box of standard dimensions.
However, such an arrangement has the disadvantage that the secondary heat exchanger must be positioned in an extremely accurate manner within the water box, so that the two orifices in the wall of the latter can be strictly aligned with the two seatings of the secondary heat exchanger to enable the two coupling tubes to be subsequently fitted. This relative positioning must be effected before, and maintained throughout, the operation of fitting the two coupling tubes.